1. Field of the Invention
This invention relates to high frequency scanning radar antenna systems and, particularly, it relates to a radar scanner which operates without the need for rotary joints in rotating assemblies.
2. Discussion of the Prior Art
Antennas used in radar scanning and communications systems generally scan by means of a rotary pedestal or rotary joint which supports the antenna structure. Thus, in the past, such systems have had to resort to a separate rotary RF joint for each beam in order to pass the microwave signal between the antenna and the signal processing electronics. In most shipboard antenna installations the weight of the antenna itself becomes of special significance. Since the antenna and its feed normally are mounted aboard the rotating pedestal, the microwave (or millimeter wave) energy must either be transmitted by means of an RF rotary joint or be generated by devices located on the antenna. Processing the radar signals by devices located on the antenna or by resort to rotary RF joints is undesirable because of such factors as objectionable topside weight and the problems encountered when performing maintenance on electronic components located high above the deck. One important factor in the design and installation of shipboard antenna systems is the recognition that low-altitude targets may be detected at greater distances with antennas mounted relatively high in the mast with respect to the surface and that detection by line-of-sight ranges increases markedly when the height of the installation is brought to a maximum.
The present invention alleviates the problems by providing a scanning radar antenna in which the weight to be rotated is reduced, which operates without the need for a stabilized rotary platform, and which can conveniently be installed with radome cover on the ships mast for reduced blockage. Most importantly, the movable plane reflector of the type used, for example, in the azimuth scanning antenna shown in U.S. Pat. No. 3,916,416 has been replaced with a planar reflector which accomplishes its function without the need for a rotary joint.